From: | Alexander Korotkov <aekorotkov(at)gmail(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Noah Misch <noah(at)leadboat(dot)com>, Nathan Boley <npboley(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Collect frequency statistics for arrays |
Date: | 2012-03-01 14:57:17 |
Message-ID: | CAPpHfdu3tSp0d=APy6swyG4H1d9JpkSEPYZ_JjqZh=V+-L9ZYA@mail.gmail.com |
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Lists: | pgsql-hackers |
On Thu, Mar 1, 2012 at 1:19 AM, Alexander Korotkov <aekorotkov(at)gmail(dot)com>wrote:
> On Thu, Mar 1, 2012 at 1:09 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
>> That seems like a pretty narrow, uncommon use-case. Also, to get
>> accurate stats for such queries that way, you'd need really enormous
>> histograms. I doubt that the existing parameters for histogram size
>> will permit meaningful estimation of more than the first array entry
>> (since we don't make the histogram any larger than we do for a scalar
>> column).
>>
>> The real point here is that the fact that we're storing btree-style
>> stats for arrays is an accident, backed into by having added btree
>> comparators for arrays plus analyze.c's habit of applying default
>> scalar-oriented analysis functions to any type without an explicit
>> typanalyze entry. I don't recall that we ever thought hard about
>> it or showed that those stats were worth anything.
>>
>
> OK. I don't object to removing btree stats from arrays.
> What do you thinks about pg_stats view in this case? Should it combine
> values histogram and array length histogram in single column like do for
> MCV and MCELEM?
>
Btree statistics for arrays and additional statistics slot are removed from
attached version of patch. pg_stats view is untouched for while.
------
With best regards,
Alexander Korotkov.
Attachment | Content-Type | Size |
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arrayanalyze-0.13.patch.gz | application/x-gzip | 22.9 KB |
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